Resistor values in colour
The colour convention Mega value

Resistors are electrical devices that are used in circuits to vary current. Because they can have very low values or very high values, it is not easy to write the resistance on the resistor itself. Instead, a system of colour coding has been devised.

Resistors are very cheap and can be bought at any electronics shop. A valuable maths and science project can be to work out resistance values from the colours on the resistors.

The colour convention
The colour bands around the resistor each represent a number. The colours represent:

Black = 0
Brown = 1
Red = 2
Orange = 3
Yellow = 4
Green = 5
Blue = 6
Violet = 7
Grey = 8
White = 9

You might find it easier to remember if you notice that the colours for numbers 2 to 7 are also "colours of the rainbow". There are two other colours that shows how precise the resistor value is: a gold band means the tolerance is +/- 5%; silver means +/- 10%; no fourth band means +/- 20%. On some resistors you may see a brown band (+/- 1%) or a red band (+/- 2%) for the tolerance. Basically, the lower the percentage tolerance, the closer the resistor will be to the stated value. View the resistor as shown in the diagram and read off the numbers from left to right. The precision band is the closest to the centre of the resistor.

Click for larger image As an example, the resistor here has bands of brown, yellow, red and silver.

The first two bands are the first and second digits, in this case 14. The third band shows how many zeros there are. In this case there are two zeros, so the value of this resistor is 1400Ω. The silver band indicates a tolerance of +/- 10%, so this resistor can be anywhere between 1260Ω and 1540Ω.

Mega value
Sometimes numbers have lots of zeros, so a prefix (fixed to the front) is used to make it easier to write. Prefixes usually used for resistors are kilo- and mega-. Kilo means one thousand and mega means one million. One thousand ohms is called a kilohm, and a million ohms is called a megohm. The units are kΩ and MΩ.

As an example 15 000Ω = 15 × 1000W = 15 KΩ.

Copyright owned by the State of Victoria (Department of Education and Early Childhood Development). Used with Permission.

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Resistor Tolerance